Description and History

NPL Listing History

NPL Status: Final

Proposed Date: 10/15/84

Final Date: 07/22/87

Deleted Date:

The site was constructed in about 1970 and is located at 3050 Bowers Avenue, a light industrial and commercial area of Santa Clara. A large industrial building occupies most of the site. Most buildings in the vicinity are low-rise developments containing office space and research and development facilities. The facility has been used to manufacture equipment for the fabrication of semiconductor wafers from 1974 to the present. During the 1970s, Volatile Organic Compounds (VOCs) were used as industrial solvents for cleaning and degreasing. Acids, caustics, and other chemicals were also used at the facility. The site is located in the Santa Clara Valley, a structural basin filled with marine and alluvial sediments. The natural groundwater flow direction beneath the site is to the north towards San Francisco Bay. Municipal water supply wells tap an extensive, deep, regional, confined aquifer that lies generally greater than 200 to 300 feet below ground surface (bgs).

Groundwater at the site is contaminated with Volatile Organic Compounds (VOCs), primarily of 1,1,1-trichloroethane (1,1,1-TCA), 1,1-dichloroethane (1,1-DCA), and 1,1-dichloroethene (1,1-DCE). In November 1983, VOCs were discovered in a monitoring well down gradient from three Underground Storage Tanks (USTs) on the west side of the large building. Site investigation began shortly after the contamination was discovered. Groundwater monitoring and extraction wells were installed and groundwater extraction began in November 1984. In January 1985, Applied Materials removed the tanks, excavated the contaminated soils, and constructed a groundwater extraction pit.

The site overlies the Santa Clara Valley groundwater basin. Groundwater from this basin provides up to 50% of the municipal drinking water for over 1.4 million residents of the Santa Clara Valley. The site became a Superfund site primarily because of the past chemical releases' potential threat to this valuable groundwater resource.

Contaminants and Risks

Contaminated Media

Groundwater

Groundwater contains VOCs such as trichloroethylene (TCE). The contaminants in the groundwater could pose a threat to human health if the groundwater is used as a source of drinking water in the future. Presently, there do not appear to be any threats associated with exposure to these contaminants, because area drinking water wells have not been affected by the contaminant plume. Soils were thought to contain VOCs, but studies have shown that they are not contaminated.

Who is Involved

Investigation and Cleanup Activities

Initial Actions

Initial Actions: In 1984, Applied Materials installed a system to pump and treat contaminated groundwater. The system consists of three extraction wells, an extraction pit, and a dual-column air stripper. In 1985, underground storage tanks and some of the surrounding soil were excavated, and an excavation pit was built. In addition, a down-gradient extraction well and a second deep monitoring well were installed to determine the extent of contaminant migration. When the groundwater treatment plant was operating,the treated groundwater was discharged to a storm drain system, which flows into San Tomas Aquino Creek and South San Francisco Bay.

Remedy Selected

Soil: In 1990, under the direction of the San Francisco Regional Water Quality Control Board, the potentially responsible parties began a study of the hazards posed by contaminated soil beneath the manufacturing facility. In 1993, it was determined the surface soils are not contaminated and thatthe saturated soils under the building would be cleaned through the groundwater remedy.

Cleanup Ongoing

Groundwater: Under state supervision, Applied Materials completed an investigation into the extent of groundwater and soil contamination at the site. In 1990, the EPA chose to continue using the existing pump and treat system, installed in 1984, to remove contaminants from the groundwater. Groundwater extraction began in 1985 and continued through 2002 until contaminant concentrations in groundwater approached declining, asymptotic levels. The pump and treat system operation was discontinued in 2002. Chemical attenuation and plume stability monitoring is ongoing.

Cleanup Results to Date

Construction of all cleanup remedies is complete. Groundwater extraction began in 1985 and continued through December 2002 when the extraction system was discontinued due to declining contaminant concentrations. Since 2002, monitoring of the plume stability and chemical attenuation processes have continued.

The fourth five year review report completed in September 28, 2010, concluded that -
Currently, all monitoring data show that the contaminant concentrations continue to decrease, and with the institutional control in place to restrict the use of ground water as a drinking water source, the remedy is considered to be protective of human health and the environment. EPA is recommending continuation of annual monitoring in the four remaining wells.